Capacitors are the basic energy storage devices in random access memory devices, such as dynamic random access memory (DRAM) devices, static random access memory (SRAM) devices, and now ferroelectric memory (FE RAM) devices. They consist of two conductors, such as parallel metal or polysilicon plates, which act as the electrodes (i.e., the storage node electrode and the cell plate capacitor electrode), insulated from each other by a dielectric material (a ferroelectric dielectric material for FE RAMs).
High quality thin oxide layers of metals, such as barium-strontium-titanates and strontium-bismuth-tantalates, for example, deposited on semiconductor wafers have recently gained interest for use in memory devices. These materials have very high dielectric constants and excellent resistance to fatigue. They also have suitable properties for a variety of other uses, such as electrooptic materials, pyroelectric materials, and antireflective coatings.
Suitable metal oxides are typically delivered to a substrate in the vapor phase; however, many oxides are difficult to deliver using vapor deposition technology. Many precursors are sensitive to thermal decomposition. Also, many precursors have vapor pressures that are too low for effective vapor deposition.
Thus, there is a continuing need for methods and materials for the formation of layers on substrates. This is particularly true for the formation of metal oxide layers, as well as other layers, on semiconductor structures, particularly random access memory devices, using vapor deposition processes. There is a particular need for methods that use volatile liquid precursors of low valent metals, which are suitable for use in vapor deposition processes without undue particle formation.